RELATIVE ROLE OF EUKARYOTIC AND PROKARYOTIC MICROORGANISMS IN PHENANTHRENE TRANSFORMATION IN COASTAL SEDIMENTS

The relative role of eukaryotic versus prokaryotic microorganisms in p henanthrene transformation was measured in slurries of coastal sedimen t by two different approaches: detection of marker metabolites and use of selective inhibitors on phenanthrene biotransformation. Phenanthre ne biotransformation was measured by polar metabolite formation and CO 2 evolution from [9-C-14]phenanthrene. Radiolabeled metabolites were t entatively identified by high-performance liquid chromatography (HPLC) separation combined with UV/visible spectral analysis of HPLC peaks a nd comparison to authentic standards. Both yeasts and bacteria transfo rmed phenanthrene in slurries of coastal sediment. Two products of phe nanthrene oxidation by fungi, phenanthrene trans-3,4-dihydrodiol and 3 -phenanthrol, were produced in yeast-inoculated sterile sediment. Howe ver, only products of phenanthrene oxidation typical of bacterial tran sformation, 1-hydroxy-2-naphthoic acid and phenanthrene cis-3,4-dihydr odiol, were isolated from slurries of coastal sediment with natural mi crobial populations. Phenanthrene trans-dihydrodiols or other products of fungal oxidation of phenanthrene were not detected in the slurry c ontaining a natural microbial population. A predominant role for bacte rial transformation of phenanthrene was also suggested from selective inhibitor experiments. Addition of streptomycin to slurries, at a conc entration which suppressed bacterial viable counts and rates of [methy l-H-3]thymidine uptake, completely inhibited phenanthrene transformati on. Treatment with colchicine, at a concentration which suppressed yea st viable counts, depressed phenanthrene transformation by 40%, and th is was likely due to nontarget inhibition of bacterial activity. The r elative contribution of eukaryotic microorganisms to phenanthrene tran sformation in inoculated sterile sediment was estimated to be less tha n 3% of the total activity. We conclude that the predominant degraders of phenanthrene in muddy coastal sediments are bacteria and not eukar yotic microorganisms.